1. Field of the Invention
The present invention relates generally to filters for purifying fluids and more particularly to filters for vehicles including aircraft where weight is a critical parameter.
2. State of the Art
Filters are used for many applications to purify fluids. One such application is the removal of noxious or poisonous gases from air by chemical defense filters. These filters can be either made small enough to be portable to be carried by an individual in a gas mask filter, for example, as disclosed in U.S. Pat. No. 2,537,992, or may be made larger for cleaning air for one or more individuals in a collective protection enclosure.
Another example of a portable filter is disclosed in U.S. Pat. No. 3,731,678. This patent discloses a smoke inhalation protector for removing or reducing smoke and other noxious fumes from the air. This device contains two one-way valves that open or close, depending on inhalation or exhalation. The device also contains a canister for containing an adsorbent to adsorb smoke and other noxious gases, as well as converting carbon monoxide into carbon dioxide.
Examples of specialized filters for treating specific fluids include U.S. Pat. No. 3,178,025 which discloses a filter element for filtering and conditioning dry cleaning solvent. The filter contains an inner cartridge of an adsorbent and an outer shell of a folded paper filter.
In U.S. Pat. No. 3,542,199, a reverse osmosis water purification unit is disclosed. The unit comprises a casing containing a semipermeable membrane cartridge with brine flow control in the form of a pair of connected restrictive conduits.
U.S. Pat. No. 3,957,469 discloses a filter cassette with removable capsule usable for the measurement of respirable and airborne dust which may be present in mines, factories and the like.
In U.S. Pat. No. 4,087,363, a filter for blood containing a series of chambers is disclosed. Between each of the chambers are diaphragms having varying pore diameters for filtering various blood components.
U.S. Pat. No. 4,102,785 discloses an inside-to-outside flow filter tube comprising a series of concentrically disposed filter media. The filter tube of this patent finds use as a filter for exhaust gases, such as for exhaust gases of internal combustion engines.
Examples of collective protection filters include the M48 which was developed by the U.S. Army Chemical Systems Laboratory (now called the Chemical Research, Development and Engineering Center), Aberdeen Proving Grounds Edgewood Area, Maryland and its contractor Honeywell Inc., Tactical Support Operations under contract DAAK11-80-C-0066, and produced under Specification No. EA-F-1284. These filters are used to protect modern tanks and other pieces of equipment and collective protection enclosures. These filters are typically cylindrically shaped and utilize a radial flow pattern. The air enters from one end of the filter, fills a hollow tube in the center of the filter, flows radially outward through a paper HIGH EFFICIENCY PARTICULATE AIR (HEPA) filter, through a bed of Whetlerite charcoal, through an annular space to the opposite end of the filter where it exits through an outlet. The material of construction for the housing containing these filters is typically aluminum. A 6061-0 aluminum is normally specified due to its formability, weldability and lower cost. However, the tensile strength for a 6061-0 aluminum is relatively low. This limits the operating pressure of lightweight, thin wall aluminum filters. Normally, the M48 and other similar chemical defense filters operate at only a few inches of water pressure. This low operating pressure inherently limits the flow through the filter.
A filter having low weight and volume combined with high fluid pressure and high fluid flow rate is desirable to meet the needs for use in aircraft and other vehicles. Also, a filter that may be assembled without welding, soldering or adhesively joining major joints or seams is desired to improve the ease of assembly and to lower the cost.